Dream Recall upon Awakening from Non-Rapid Eye Movement Sleep in Older Adults: Electrophysiological Pattern and Qualitative Features

Abstract

Several findings support the activation hypothesis, positing that cortical arousal promotes dream recall (DR). However, most studies have been carried out on young participants, while the electrophysiological (EEG) correlates of DR in older people are still mostly unknown. We aimed to test the activation hypothesis on 20 elders, focusing on the Non-Rapid Eye Movement (NREM) sleep stage. All the subjects underwent polysomnography, and a dream report was collected upon their awakening from NREM sleep. Nine subjects were recallers (RECs) and 11 were non-RECs (NRECs). The delta and beta EEG activity of the last 5 min and the total NREM sleep was calculated by Fast Fourier Transform. Statistical comparisons (RECs vs. NRECs) revealed no differences in the last 5 min of sleep. Significant differences were found in the total NREM sleep: the RECs showed lower delta power over the parietal areas than the NRECs. Consistently, statistical comparisons on the activation index (delta/beta power) revealed that RECs showed a higher level of arousal in the fronto-temporal and parieto-occipital regions than NRECs. Both visual vividness and dream length are positively related to the level of activation. Overall, our results are consistent with the view that dreaming and the storage of oneiric contents depend on the level of arousal during sleep, highlighting a crucial role of the temporo-parietal-occipital zone.

<p>Electrophysiological Correlates of Dream Recall During REM Sleep: Evidence from Multiple Awakenings and Within-Subjects Design</p>

“…26 In this vein, several studies revealed the relationship between higher cortical arousal during NREM sleep (increased fast-frequencies and/or reduced slow-frequencies) and DR both in healthy and clinical groups. 5,8,9,11,12 Besides, we confirmed that the parietal and occipital regions are involved in sleep mentation, as suggested by early studies. 27 Consistently, Eichenlaub and collaborators 18 revealed that high dream recall frequency was associated with increased activity in the temporo-parietal junction at rest.…”

“…Our findings on EEG correlates of DR during REM sleep overlap the EEG pattern observed during NREM sleep, 5,8,10,11 providing support to the one generator model of mental sleep activity. 26 In this vein, several studies revealed the relationship between higher cortical arousal during NREM sleep (increased fast-frequencies and/or reduced slow-frequencies) and DR both in healthy and clinical groups.…”

“…Previously, this index was proved to be reliable predictor of dream recall both in healthy and clinical samples. 8,10 The 2×2 ANOVA recall × time was carried out also for the delta/beta power ratio values, for each scalp derivations. To adjust the α level Bonferroni correction was applied.…”

“…Studies on neural correlates of dream experience suggested the potential influences of circadian, ultradian, and homeostatic factors on dream features. 1 Most investigations neglected the impact of these variables on EEG predictors of dream recall (DR) [2][3][4][5][6][7][8] and very few studies provided information about this issue.…”

Dreams, Sleep, and Psychotropic Drugs

“…It is also now clear that the complexity and story-like characteristics of dream reports are related to sleep stages but also, and even more so, to circadian rhythms leading to more vivid and complex dreams in the morning than in the early night [e.g., (13)(14)(15)]. Recent developments have provided strong experimental arguments in favor of the arousal-retrieval model (16), proposing that awakenings when dream content is still in short-term memory are necessary to encode dreams into longterm memory (17)(18)(19)(20)(21)(22)(23).…”